Fixes test broken by r3176 (#4439).
Icons updates and cleaning.
Added missing translation for permission_view_issues (#4415).
Group icon changed on project members list.
IE8 fix.
Removes large icons.
Do not hide scroll buttons if some tabs are still hidden.
Adds auto overflow to content div.
Adds an admin layout that displays the admin menu in the sidebar.
Adds a Plugin API to allow one plugin to depend on another.
